1. Field of the Invention
The present invention relates generally to a hand tool, and more particularly to a torque screwdriver.
2. Description of the Related Art
FIGS. 1 and 2 show a conventional torque tool 10. The torque tool 10 includes a main body 12. Two sides of the main body 12 are respectively formed with two cavities 13. A top end of an operation stem 14 is pivotally rotatably connected in a shaft hole 121 of the main body 12. The circumference of the operation stem 14 is formed with six teeth 15 and six locating troughs 16 between the six teeth 15. Two elastic abutment assemblies 17 are disposed in the two cavities 14. Each elastic abutment assembly 17 includes a steel ball 18 and a spring 19. The spring 19 applies an elastic force to the steel ball 18 to make the steel ball 18 elastically abut against the circumference of the operation stem 14.
In general, the steel ball 18 is positioned in the locating trough 16 as shown in FIG. 2. The torque tool 10 is used to screw a screw or a nut or the like. When the torque of the tool is about to reach a set torque value, the spring 19 is compressed as shown in FIG. 3. At this time, the steel ball 18 is moved along the tooth face 151 of the tooth 15 to the tooth crest and the main body 12 is rotated around the operation stem 14. When the steel ball 19 is moved to the tooth crest, the tool 10 provides a maximum torque. In the instant of reaching the maximum torque, the steel ball 18 slides over a tooth 15 to fall into the next locating trough 16 and restore to the state as shown in FIG. 2. The click of falling into the locating trough 16 can alert a user that the torque of the tool has reached the set torque value.
The above torque tool 10 is a two-way torque tool, which can be operated clockwise and counterclockwise. However, in order to operate the torque tool 10 in two directions, the width of the tooth 15 is narrowed so that the tooth face 151 is quite steep. The tooth face 151 has a large slope and quite short length. Therefore, when reaching the set torque value, the steel ball 18 will abruptly move from the tooth valley, (that is, the locating trough 16 as shown in FIG. 2), to the tooth crest in a very short time. Also, the spring 19 is abruptly compressed in a very short time. Therefore, in operation of the tool, the torque of the tool will instantaneously greatly change. As a result, the torque tool can hardly provide a precise torque.
Furthermore, as shown in FIG. 1, the top end of the operation stem 14 of the tool 10 is pivotally disposed in the shaft hole 121 of the main body 12. The operation stem 14 is not well supported and is likely to shake. Also, the operation stem directly abrades the wall of the shaft hole 121 against a great frictional force. Therefore, the torque value of the conventional torque tool is unstable and the torque tool can be hardly smoothly operated.
In addition, the tool has no waterproof design so that the internal components are apt to rust or culture bacteria. In this case, the tool cannot be used in an environment requiring high sanitary condition.